Question

1. Imagine a scenario is which 104 protons are pumped across the membrane of the inner mitochondrial membrane. If you assume that the glycerol-3-phosphate shuttle is used, and the overall yield of substrate-level phosphorylations is 5,
   1. Describe what role the electrons play and describe the general movement of the electrons through the electron transport chain to the final electron acceptor. (5 pts)
   2. What would the effect of adding dinitrophenol (DNP) be on the electron transport chain? Be specific. (3 pts)
   3. How many total ATP would be made under aerobic conditions starting at the molecule you determined? (5 pts)
   4. Finally, how many protons would be pumped from your starting molecule under anaerobic conditions and why? (2 pts)

Answer 1

Answer to above question

a) An electron transport chain (ETC) is a site of oxidative phosphorylation is found on the inner mitochondrial membrane. It is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane.

Flow and role of electron is as follows -

NADH+H^+ COMPLEX I QCOMPLEX III CYTOCHROME C COMPLEX IV HO

                                    

                                   COMPLEX II

                                          

                            SUCCINATE

Complex I - Here two electrons are carried to the first complex aboard NADH. This complex, labeled I, is composed of flavin mononucleotide (FMN) and an iron-sulfur (Fe-S)-containing protein. The enzyme in complex I is NADH dehydrogenase and is a very large protein and it can pump four hydrogen ions across the membrane from the matrix into the intermembrane space, and it is in this way that the hydrogen ion gradient is established and maintained between the two compartments separated by the inner mitochondrial membrane.

Q and Complex II - Complex II receives FADH2, which does not pass through complex I. Compound connecting the first and second complexes to the third is ubiquinone (Q).When it is reduced, (QH2), ubiquinone delivers its electrons to the next complex in the electron transport chain. Ubiquinone receives the electrons derived from NADH from complex I and the electrons from FADH2 from complex II, including succinate dehydrogenase.These electrons bypass and thus do not energize the proton pump in the first complex, fewer ATP molecules are made from the FADH2 electrons.

Complex III - Third complex is comprises of cytochrome b, another Fe-S protein, Rieske center (2Fe-2S center), and cytochrome c proteins; this complex is also called cytochrome oxidoreductase. Complex III pumps protons through the membrane and passes( allow it to move) its electrons to cytochrome c for transport to the fourth complex of proteins and enzymes.

Complex IV - Fourth complex is made up of cytochrome proteins c, a, and a3. Complex contains two heme groups and three copper ions. The cytochromes takes up an oxygen molecule very tightly between the iron and copper ions until the oxygen is completely reduced. This reduced oxygen picks up two hydrogen ions from the surrounding medium to make water (H2O). Removal of the hydrogen ions from the system contributes to the ion gradient used in the process of chemiosmosis.

b) Compound 2,4-dinitrophenol (DNP) acts as ionophore(proton) , it binds protons on one side of a membrane, and being fat-soluble it travels to the opposite side where it loses the protons and thus disturbs proton gradient reducing ATP Synthesis.So what we eat is used in ATP synthesis and we reduce weight too slowly slowly.So DNP will act as a inhibitor for syntheis of ATP and thus could be dangerous for life.